The ring airfoil is really the only ‘new’ and technologically advanced projectile technology in the last 400 years. In fact, the traditional mathematical descriptions of a projectile and its ‘flight’ do not apply. This is because a ring airfoil projectile is not a real projectile in any sense, other than possibly that it can be launched from a gun, it is a lifting body or more precisely a glider. In all, the performance and possibilities offered by a ring airfoil glider are very enticing.
Ring airfoil technology is particularly advantageous for less lethal applications. Usually, these non-penetrating projectiles must have a large frontal area and very low mass to limit undesired human vulnerability effects. In conventional projectiles this equates with very poor ballistic performance and the need for higher than acceptable close range danger of injury and lower than desired effectiveness at the long ranges presented by riot control and military operations. Conversely, the ring airfoil naturally fits the less lethal tactical situation perfectly: light with large effective frontal area with phenomenal ‘down range’ properties.
Ring airfoil gliders (RAGS) are tubular-shaped wings which fly or glide through the air much like a conventional winged glider. Unlike a conventional ballistic projectile, the ring airfoil glider produces lift which gives it a much flatter trajectory. Depending on the design and launching parameters of the glider, the lift results in the glider rising to only small fraction of the height of the trajectory of a conventional ballistic projectile at the same range. The lifting capability reduces or eliminates the problem of range estimation errors and allows ring airfoil gliders to achieve higher hit probabilities at long range than all other candidate low lethality or grenade projectiles.
Conventional ballistic projectiles have their longitudinal axis oriented along their flight path. As the projectile travels through its curved ballistic flight path the projectile changes its attitude or orientation from its original line of departure to align with its flight path. Projectiles have a parabolic shaped curved flight. Conversely, the ring airfoil glider has strong gyroscopic forces induced by spinning the projectile/glider's mass, concentrated near its outer circumference. The gyroscopic stability maintains its original launch orientation (along its line of departure). As a ring airfoil glider proceeds along its trajectory and begins to fall under the pull of gravity, the flight path starts to curve downward toward the ground. Therefore, the glider becomes canted in relation with the airflow over its wing surface causing lift forces to be created on it in the direction opposite to the gravitational pull. This functions exactly like increasing the pitch of a helicopter's rotor, which is also airfoil shaped, to increase the rotor's lift. Although, the ring airfoil has a slight curve in its flight path until it stalls, at which point it drops rapidly, it appears to the casual observer to travel a straight line and then suddenly fall to the ground. Ufano, a contemporary of Galileo nearly five hundred years ago, wrongly thought conventional projectiles traveled like this. The flat trajectory of the ring airfoil is a primary advantage over conventional projectiles.
It should be noted that this ‘pitch’ change increases aerodynamic drag on the ring airfoil glider. As the airfoil is traveling at an angle to the airflow, not only is its presented area increased, but the airflow over it is bent more to cause increase in its lifting force and increasing its induced drag; induced drag is caused by the energy which is expended due to the bending of airflow around the airfoil resulting in lift and the associated airflow separation at the trailing edge of the airfoil as its angle of attack is increased or pitch increases. Simply stated, the ring airfoil glider converts some of its momentum to lifting forces at the expense of its forward velocity. However, in comparison to a conventional projectile a ring airfoil's drag is a very tiny fraction.
For comparison purposes, consider:
The less lethal M-1006 Sponge Grenade 40 mm round recently developed by David Lyon at ARL (Army Research Laboratory) now Edgewood RD&E Center in Aberdeen, Md. with help from Frank Dindl at TACOM-ARDEC at Picatinny Arsenal, N.J. out of programs of 30 years ago. It is a conventional ammunition projectile with low drag, short flight times and just acceptable human vulnerability effects. It would be very difficult to improve on its performance using conventional projectile technology.
The RAG M743 projectile (glider) developed by Abe Flatau and his group at ERDEC (the Edgewood RD&E Center) some 30 years ago serves to illustrate the contrast between conventional and lifting projectiles.
A general comparison is as follows:
Conventional Projectile vs. Ring Airfoil Glider Flight CharacteristicsAll projectiles 35 gramsPlus RAG M743Sponge GrenadeRAG M743(Equivalent Muzzle Velocity(Std. Muzzle Velocity)(Std. Launch Velocity)to Sponge Grenade)DistanceMuzzle75 metersMuzzle75 metersMuzzle75 metersVelocity82 m/sec52 m/sec60 m/sec50 m/sec82 m/sec67 m/secTime of Flight—1.12 sec—1.36 sec—1.00 secMid-Range111.625—0.75—0.55Trajectorymetersmeters
In spite of its converting momentum to lift, the M743 loses only 10 meters/sec, compared to the Sponge Grenade's 30 meters/sec. loss over the same distance. The change in speed results in a corresponding square law change in kinetic energy, i.e. change in the human vulnerability results. In addition, the lower speed RAG experiences only half the trajectory height, while the higher speed RAG is less than a third of the trajectory, even though the Sponge Grenade has a 0.24 second lower time of flight; i.e., less time to be deflected by gravity.
Generally, the higher the peak trajectory (above the line of sight), the more difficult it is for the shooter to hit a target: due to his need to estimate how much to compensate for the projectile's drop—a task made more difficult when like a soldier is under fire. A useful concept in measuring the necessity of accurate range estimation is the ‘danger space.’ The danger space is the distance over which the projectile remains within a man's height. If the projectile's velocity is low with a corresponding long flight time, the trajectory curves steeply, and there will be a portion of the range for which the projectile will pass harmlessly over a man's head. In this case, the danger space consists of nearby ranges where the projectile is still within a man's height and the last part of the trajectory, as the projectile falls within the man's height before ending in the projectile's contact with the ground. The latter portion is shorter, as the trajectory is steeper at the end. And, for less lethal devices like the sponge grenade the nearby ranges are not usable due to the increased risk of unacceptable injuries.
With a flat trajectory like that of the ring airfoil glider, this ineffective zone within the defined effective range disappears, leaving one continuous danger space from muzzle to the target. This allows the shooter to quickly acquire the target without the need for sophisticated (and fragile) range finders and computers that are useless when the battery runs down—or the hardware or software malfunctions.
Cross wind performance for less lethal kinetic ammunition projectiles has always been problematic. This is due to less lethal lightweight large diameter projectiles having low sectional density and low launch speeds, i.e. easily pushed around by the wind, combined with high velocity degrades resulting in long flight times, i.e. time to be deflected by the wind. Generally, the ring airfoil helps to alleviate these problems by decreasing the flight time. However, the lifting effect of the ring airfoil does partially come into play with cross winds, much like what happens with its drop characteristics. For wind blowing against the glider at low angles of attack, less than 10″ to 15O, the lifting force causes the glider to be deflected less than usual for a conventional projectile. As the wind angle increases the lift effect tapers off until it is not present, at which point the projectile behaves like a conventional projectile, although it has a lower flight time. As the wing angle passes beyond ninety degrees and becomes a tail wind at shallow angle, less than 10′ to 15″, the glider slightly increases its deflection but this is offset by the reduced airspeed, when traveling with the wind, and the lower flight time. Practically to the shooter, this behavior is not usually perceived as either worse or better than a conventional projectile's performance due to the fact that he has no direct comparison to the round he is presently firing. Wind deflection, other than in artillery, is a guessing game for the soldier in the field; he has no means of measuring wind velocity knowing its precise direction and the time to calculate wind deflection when he fires the weapon-he can only compensate for the next shot, after observing the impact point of the round.
The one requirement for the near-ideal trajectory characteristics of ring airfoil gliders is that the gyroscopic forces and the aerodynamic lifting forces should be longitudinally centered at the same point on the airfoil's section. The U.S. Army's M742 & M743 are examples of the ring airfoil glider with unbalanced lift and gyroscopic forces. [It should be noted all less than lethal use ring airfoil projectiles/gliders subsequent to the M7421743 are copies of those devices, except for the present inventor. This is due to the difficulty in developing a new ring airfoil design, the practical problem and expense of proving its human vulnerability safety, and that the technology's originator and leading proponent, Abe Flatau, having been heavily relied on as consultant to every subsequent developer.
The U.S. Army's M743 Sting RAG and M742 Soft RAG (gliders, see FIG. 1) were designed with an aft center of gravity (inherently unstable) to allow the installation of CS tear gas packets in pockets evenly spaced around the forward outside diameter of the glider. The CS packet's mass made for a more balanced downrange flight path in the original M742 Soft RAG; both are based on the same molded rubber ring airfoil design. The M743 Sting RAG suffered from the loss of this payload mass, as it made it tail heavy. The imbalance between the center of pressure and center of gravity combined to create a moment arm on the RAG glider. In flight, the lift forces acting through the moment arm cause the RAG glider to become canted in a lateral direction in relation to the airflow and gravity. This, in turn, causes the glider to behave like a curve-pitched baseball.
In addition, the cross section of the M7421743 RAG glider is not an ideal airfoil: It is molded of rubber with rough mold flashing left in place at critical places for airflow. Adding to the problem, it is wound with a relatively rough paper cover: needed to prevent centrifugal forces from deforming the flexible rubber glider and to hold the CS packets in place in the M742 Soft RAG. Additionally, the flat topped and rectilinear CS pockets on the airfoil's outside high point, an area that should have been curved, made the M7421743 less than an ideal airfoil section. All these factors contributed to relatively high drag coefficients and associated velocity degrade characteristics. The lift force disproportionably decreases and changes position along the length of the M7421743 airfoil section as the glider slows down, increasing the angle of attack and resulting in a progressively more unbalanced glider flight configuration. This change of balance between the forces causes an undesirable increase in this glider's trajectory curvature at ranges over 60 meters. It is due to the concerted effort of Abe Flatau and his staff at the Army's ERDEC lab that the M7421743 worked as well as it did, while meeting the conflicting requirements they were given. The balance struck on the M7421743 limited it to a narrow launch window of spin rate and velocity to achieve its goals over the desired distance. To complete the story, the preferred M742 Soft RAG projectile's packets of CS tear gas had a small unavoidable variance in weight. This, in turn, created a gyroscopic imbalance in the spinning projectile. This imbalance increased the dispersion and further degraded the accuracy of the M742 Soft RAG. Poor dispersion and limited shelf storage life of the CS fill combined with its high cost of production doomed the M742 Soft RAG. It was type-classified for production but not produced in quantities beyond that required for testing (a few hundred). The M743 Sting RAG was produced for inventory, about 500,000 units, but never issued. Ultimately, the reasons for the failure of the original non-lethal RAG have to do more with the politics of the time rather than technical inadequacies as the M742 and M743 and their associated M234 launcher attachment for the M-16A1. Simply, they really did meet and exceed all their original requirements—it's just their mission was a political illusion.
Back to Ring Airfoil Technology
In less than lethal projectile technology there is a trade-off between the poor aerodynamics of the large cross-sectional area projectile weapons required to prevent the blunt trauma weapon from being a penetrating one and the need for acceptable ranging and flight characteristics. The key to the ring airfoil glider projectile's superior aerodynamic and terminal performance is the trade off between its cross-sectional area and the density of the medium in which it travels.
Ring airfoil gliders have excellent aerodynamic drag properties due to their streamlined shape and low cross-sectional area. The fluidity and low density of air drastically reduces drag forces on a ring airfoil glider as the air simply passes through the center of the projectile, rather than traveling around the entire projectile's perimeter. On the other hand, a ring airfoil glider encountering flesh has a very low ballistic coefficient, as flesh is a high density, viscous, elastic solid. Flesh cannot flow through the hole in the center of the ring airfoil glider at the practical speeds that a less lethal ring airfoil travels. Therefore, the ring airfoil glider's energy is dissipated on the surface over an area encompassed by the outside diameter of the projectile, an area much larger than its aerodynamic cross-section. This phenomenon was demonstrated during the extensive biophysical work done on the Army's M742 and M743 RAG projectiles at ERDEC. These results were obtained in testing the device against various live animal targets at impacts from low velocity were no injury was produced to high velocity impact where death was a certainty.
Ring airfoil gliders have excellent aerodynamic drag properties due to their streamlined shape and low cross-sectional area. Be this as it may, the very simple basis for the ring airfoil's improved effectiveness is that it has a dual effective sectional density. The sectional density when considered over the outer diameter of the ring airfoil is very low and this is what is important in limiting dangerous injuries and how it performs in analysis of blunt trauma. [Conventional projectiles only function from this basis outer diameter sectional density for both their flight and impact properties, a conventional less lethal projectile can be soft or ‘expand’ on contact but this limits both its blunt trauma rating and its pain production, i.e. low effective contact pressure. One wonders why a soft projectile would be considered, for any less lethal, as it only decreases the effectiveness of the projectile in producing pain and can lead to actually increasing the danger due to higher than needed levels of energy—reduces efficiency in engineering parlance. If one takes notice, all less lethal projectiles that are reasonably safe do not break the skin, hard or soft.]
The real advantage is the second sectional density of the ring airfoil: that based on its aerodynamic presented area. Although, the mass is the same the presented area is significantly less than its outer diameter area. This presented area sectional density reduces its flight drag, and it increases its contact pressure on a target where it actually contacts the target-its leading edge. Thereby, the efficiency of the ring airfoil for less lethal use is very much higher than for any conventional projectile.
The pockets formed in the M742tM743 ring airfoil gliders helped to meet the biophysical requirement of essentially zero lethality or injury, even for head impacts [goals based on anticipated use on minors during population control missions in the USA; a fallout requirement from the Kent State riots]. If the M7431M742 are launched as in the forgoing example at the same muzzle velocity as the sponge grenade the injury or lethality produced would be very greatly less than the sponge grenade. The M742 and M743 RAG projectiles were designed under very strict safety requirements—much stricter than today's automobile airbag criteria. It helped to meet the criteria to put the collapsible CS pocket section ahead of the center of longitudinal mass of the projectile; this limited the energy transfer to the target.
Although upon impact, flesh will not flow through the ‘hollow’ ring airfoil: it will “bulge” into the center opening. If looked at in section, this phenomenon deforms the flesh into a ‘W’ that stretches the skin and immediately subcutaneous tissues much more than the ‘U’ shaped deformation of a conventional rubber bullet like the sponge grenade. This ‘W’ deformation and stretching not only dissipates the energy of the projectile faster, than the ‘U’ shaped deformation, but more in the outer layers of flesh. In fact, the ‘U’ shaped deformation tends to transfer the energy deeper into the tissue which creates much more dangerous damage to vital tissues and organs. However, the ‘W’ shape creates a wider surface bruise than that produced by a conventional rubber bullet. This is good, as most of the body's pain receptors are in the skin and outer tissues.
Pain Phenomena:
A Ring Airfoil at the Same Energy Level Will Produce More Pain but Less Permanent or Life Threatening Damage than a Conventional Projectile.
A simple demonstration of how the localized stretching and deformation of the flesh is more effective than a flat blunt blow can be readily made with everyday objects. An example of similar effects in producing pain is comparing the difference between a wooden mallet with a flat and smooth face compared with a mallet like used for meat tenderizing with a coarse pattern of serration on its face. If one experiments with both mallets by smartly striking each over a range of force and speed against the flesh on the forearm, the back of the hand, or palm it will be readily apparent that the serrated tenderizer type mallet produces more pain than the plain face mallet. One will notice that even with less force, i.e. energy, the serrated mallet produces more pain. The actual area of contact is less with the serrated mallet even when the mallets are the same diameter and the impacted area is the same for both mallets. The difference in pain production is due to both the increased localized deformation and associated stretching of the skin and the comparatively sharp points of the serrations compared to the smooth face and rounded edges of the blunt mallet, and because the points create higher unit point of contact pressure.
The skin and subcutaneous structures of the body contain most of the pain receptors in the body. Blunt blows which transfer energy into deeper tissues that are more critical to life and functioning of the body but not as effective at producing pain. Also, the pain receptors most efficient at producing pain need high unit pressures to achieve the maximum pain effect [this is why a prick with a needle can create a high level of pain even though a small area is affected].
Comparatively, the serrated mallet affects more pain receptors, and the higher level of pressure in the localized areas of the serrations stimulates the high level (pressure) pain receptors more effectively. Additionally, the sympathetic nervous system dilates the capillaries in the injured area further stretching the area thereby increasing the skin temperature; this causes more localized pressure and spreads over a wider area causing more receptors to be affected while allowing rejuvenation of the originally injured nerve ends to intensify the perceived pain. The ring airfoil performs like the serrated mallet. The ring airfoil allows for significant reduction in the mass of the projectile for the same effective area proportionally reducing any blunt trauma injury while increasing the pain effect. Achieving the maximum pain effect with the smooth mallet or conventional less lethal projectile will make for a severe or life threatening injury. Additions of an irritant such a ‘pepper’ or tear gas material can extend the effects of the stinging blow provided by a ring airfoil. It should be noted, the pain phenomena and functioning of the autonomic nervous system are the least understood of all the body's systems and strangely can produce the maximum pain perceivable when very small areas of the skin are stimulated, an example: a small sharp object which does not even penetrate the skin or really injure the body other than trivially can be very painful.
A good way of determining the maximum pain effect for a kinetic energy projectile weapon, while producing minimal injury, is the point where the skin's capillaries are just ruptured to produce a persisting red rash (on magnified inspection tiny blood blisters are produced in the area) with little or no damage to deep tissues. The M7321733 ring airfoils had their performance tailored to achieve this maximum pain point over their entire effective range-muzzle to 60 to 80 meters. [The rash is a ring shaped finely speckled red area corresponding to the contact area of the ring airfoil with the skin at the point of maximum stretching]. Conventional less lethal munitions like the M-1006 cannot achieve this type of effect as their energy dump rate is too slow and they cannot stimulate the high pressure pain receptors without having very high risk of killing or permanently injuring the target. Notably, the subject inventive ammunition can deliver the same effects as the original RAG M2321233 over a significantly greater effective range.
Other Specific Ring Airfoil Technologies
Miles C. Miller, while working for Mr. Flatau's group at ARL, developed a Expendable Launcher for Non-Lethal Ring Airfoil's using the M232 and M233 RAG projectile/gliders in the 1970's. This differed from the M234 launcher attachment for the M16A1 in that they are self contained. It was made of molded plastic material and was a disposable barrel and casing round, needing no launching tube or barrel. It was designed to clip onto a modified revolver which had its barrel and cylinder removed. The sabot slid on a central rifled rod with a cone shaped sabot stop on its end. Upon firing the sabot, holding the projectile, was pushed forward by the propelling gases. At the point the sabot's trailing edge cleared the casing and released the propelling gases the conical forward end of the central rod engaged the sabot, stopping it, causing the projectile to separate and travel down range. An excellent device limited in being very expensive to manufacture, by the need for a non-standard launcher or firing mechanism, and in its use of the U.S. Army's M232 and M233 RAG projectiles 1 gliders. However, it is representative and forerunner of most successful gas powered launcher which followed.
The NIJ, National Institute of Justice, part of the Federal Government's Justice Department, has funded private ventures to develop ring airfoil toys and police less lethal ring airfoil glider launcher mechanisms. These police weapons take the form of 65 mm gliders newly manufactured and based on the gliders of the original Army M7421743 ring airfoils. The weapons launching mechanism is similar to the above using the design engineering principle of simple inversion of the design, i.e.: the sabot is spun by grooves on its outer diameter mating with spiral grooves on an outer case's inner diameter and is stopped by a simple lip on the case forward edge with the propellant being a smokeless gunpowder. This design being nearly identical the present inventor's early ring airfoil launchers, wherein compressed air was the propellant, that were publicly demonstrated for The State of California Technology Transfer Commission of the Department of Prisons in the early 1990's.
Other earlier U.S. Army programs, from the early and mid-sixties, for Ring Airfoil grenade munitions demonstrate the vast improvements this technology has over conventional weapons. Mr. Flatau's group at ARL of the time developed two experimental munition RAG grenade ammunitions. The first was a 65 mm replacement for standard shoulder-fired 40 mm grenade ammunition which improved the effective ‘kill’ radius of a standard grenade round by about SO %, while significantly improving a shoulder-fired grenade's effective range. Interestingly, the second was a 40 mm replacement for the M406 round—although, this too required a new launcher/barrel due to the stabilization spin rate difference over convention projectiles. This round had the same ‘kill’ radius of the standard M406 round but increased its effective range, shoulder-fired, from around 400 meters to over 1400 meters. With this last performance achieved at a lower loft than needed for the M406's 400 meter range. A direct comparison is at 400 meters the M39 system (M79 shoulder launcher and M406 round) needed an elevation angle of 39″ with the RAG munition needing only 6″ elevation to achieve the 1400 meters. Both of these were very simple ammunition rounds for a basically conventional gun with a special rifling pitch and had pusher sabots friction separated from the ring airfoil in flight.
Supersonic lethal tubular projectiles have been developed. These came from the earliest ideas proposed by Mr. Flatau and he and various associated are still quite active in the field. However, such devices are very critical to design and manufacture and have limited uses. These devices are usually in the form of replacement ammunition for conventional small caliber hand and long guns intended to be extraordinarily lethal over conventional ammunition. They are similar to the very early rounds and use pusher sabots which are fiction aerodynamically separated. The supersonic ring airfoil does not have as significant lift generating capability as the larger caliber subsonic non-lethal or less lethal projectiles, and therefore, is of limited improvement over conventional projectiles. And, they are usually intended for producing lethal wounds by limited penetration of the body combined with a very fast energy transfer dump resulting in very nasty gunshot wounds.
On the other end of the spectrum are the ring airfoil toys. This technology lends itself to the ‘toy gun’ field due to the inherent safety provided and the excellent range provided. Toys typically use a thin rubber, plastic or thicker foam ring and usually dispense with functional airfoil shape to save on cost as ultimate performance is not the issue but fun. Generally, a spring loaded (either steel or rubber) sled mechanism riding on a spiral groove track with a stop to stop the sled and separate the ring airfoil to flight is used. Some take the form of a throw toy designed to be hand thrown by either flipping it off the hand at the end of the throw to create some spin stabilization or with a tail mechanism used to both throw and aerodynamically stabilize the ring. In general other than the throw types, the primary objects of the toys are unique and enticing style and various repeating mechanisms or combination of several launching mechanism into one ‘gun’ to provide for repeat shots.